1. Field of the Invention
The subject invention relates to liquid dispensing apparatus, and more particularly, to a system for dispensing a metered quantity of liquid additives into a fluid flowing through a filtration system.
2. Background of the Related Art
Fluid filtration systems often require the dispensement of additives into the fluid flowing therethrough to alter or modify the characteristics of the fluid, i.e., to chemically react with the fluid so as to counteract certain deleterious effects of the fluid on the system, or supplement worthwhile characteristics that have deteriorated from the fluid over time.
For example, in an internal combustion engine, lubricating oil left untreated is often subject to deterioration caused by suspended materials such as combustion residues and particles produced by wear and abrasion of the moving engine parts. In addition, deterioration can occur from the exhaustion of preexisting additives in the engine oil. To counteract the deteriorative effects caused by the breakdown of engine oil, various mechanisms have been developed.
One such mechanism is disclosed in U.S. Pat. No. 4,075,097 to Paul which includes an oil filter having an enclosure containing a filter and a body of an oil soluble, relatively solid polymer having oil additives compounded therein. The polymer body is positioned such that it dissolves at a relatively linear rate so as to prevent concentrations of the additives during the service life of the filter. A similar mechanism is disclosed in U.S. Pat. No. 4,265,748 to Villani et al. which includes an oil filter having a tubular member containing a mixture of additives. The tubular member has at least one opening closed by a diaphragm made of a material soluble in the lubricant. In both of these prior art additive systems the additive is not introduced into the oil flow in a metered quantity proportional to the volume of oil flow through the system. In addition, there is no mechanism for preventing the dispersal of additive when the oil flow is temporarily discontinued.
Another example of a fluid system in which additives are used is the feedwater line of a convection steam boiler. In these systems, mineral scale inhibitors may be added to reduce or eliminate--depending on the mineral content in the fluid--scale in the boiler tubes. Deposits of scale in the system retard the flow of heat and raise metal temperatures. Reducing or eliminating boiler scale reduces boiler maintenance and downtime. In addition, the life of the boiler and its associated parts are prolonged. Additives may also be used in the feedwater to reduce dissolved oxygen. Since dissolved oxygen is the greatest factor in the corrosion of steel surfaces in contact with water, deaeration of makeup water and feedwater in boiler fluid systems is of utmost importance. Typically, partial deaeration is accomplished by either boiling or passing the fluid through a tray or spray-type deaerating heater. Thereafter, it is customary to supplement feedwater deaeration by adding a scavenging agent such as sodium sulfite or hydrazine to effectuate the complete removal of residual oxygen. Corrosion of the fluid system components can also occur from acidic conditions in the fluid. This can weaken the system's lines because of the loss of metal. pH altering agents may be added to counteract the acidic nature of the fluid.
Various methods have been employed to facilitate the addition of liquid additives to boiler feedwater and makeup water of fluid systems. One such method is the manual addition of additives into the makeup water storage tank of the fluid system. This method is problematic since it is difficult to completely mix the additive into the fluid and to ensure the correct proportion of additive to fluid as the proportion of additive to fluid changes each time the tank is topped off. Also, many fluid systems include utility-line feed water supplies, thereby eliminating the ability to utilize a storage tank to introduce additives in the manner described above.
Another method used in conjunction with line feed supplies is inline chemical injection systems. Exemplifying this approach is the system currently available under the tradename AQUAprep, catalog no. D2684, from Barnstead/Thermolyne Corporation, of Dubuque, Iowa. This device includes a canister having an inlet flow path and an outlet flow path and a rigid cartridge containing a quantity of chemical additive. A rigid additive flow restricter is provided at the top end of the dispenser in communication with the outlet flow path of the device. The flow restricter consists of a rigid plug constructed of a semi-porous material which has an axial bore extending therethrough of extremely small diameter. In use, as feed water flows through the device, additive is drawn from the dispenser, through the axial bore of the plug, and into the flow stream. This device has the disadvantage of not providing precise proportioning of the chemical additive. This is partly due to the partial mixing of feed water with the chemical additive in the cartridge and partly due to the inherent time-lag in the system caused by canister back-flow after periods of system inactivity. In addition, because the chemical concentration is determined by the restricter orifice, restricters must be experimented with during initial setup to obtain an acceptable initial flow rate.